Coffee is a beverage with global and growing appeal, and there is an ever-increasing demand for high quality coffee. Coffee beans must be roasted prior to brewing. Roasting is a process which causes a complex series of chemical changes in the beans wherein sugars and/or other organic compounds are pyrolized, and various volatiles are released so as to generate a complex pattern of flavor elements. In order to generate a good flavor profile, the roasting process must be very carefully controlled, in terms of time and temperature during both roasting and cooling. Under-roasted coffee produces a thin, latex-flavored, bitter beverage, while over-roasted coffee is oily and burnt tasting. Prolonged roasting, even at an appropriate temperature, volatilizes many of the flavor elements and produces a beverage of little taste. Roasting is further complicated by the fact that some of the reactions occurring during the roasting are exothermic, and as a consequence, the beans can readily become overheated even after being removed from a heat source. It will therefore be appreciated that roasting is a very complicated process, typically carried out by trained personnel.
A traditional roasting technique comprises tumbling the coffee beans in a heated drum. While the hardware for the process is relatively simple, control is difficult, and it is very easy to scorch and ruin the beans. A skilled roastmaster will control the application of heat to the drum so as to achieve a desired time-temperature roast profile; however, learning to do so is a lengthy process, and parameters which are used for one type of drum roaster will not transfer to another. Furthermore, smoke and oils generated in the process remain in contact with the beans and can confer a disagreeable taste.
As a consequence, the industry is turning to the use of fluidized bed roasters. In systems of this type, the coffee beans are at least partially levitated by a stream of heated air, and the degree of roasting is controlled by controlling the temperature of the air and the duration of the heating cycle. While fluidized bed roasters eliminate problems of contamination by smoke and oils, care must still be taken to avoid scorching the beans. Toward this end, prior art fluidized bed roasting systems typically include provisions for controlling the roast temperature and quenching the beans after they are roasted, as for example by an introduction of a stream of cool air or by spraying the beans with water. U.S. Pat. No. 4,484,064 discloses a fluidized bed coffee roaster in which ambient air is used for cooling. A somewhat similar system is disclosed in U.S. Pat. No. 5,185,171. U.S. Pat. Nos. 3,964,175 and 5,394623 both disclose the use of a water spray to cool the beans.
In all instances, the fluidized bed coffee roasters of the prior art provide only a simple roast profile in which temperature rises at a steady rate; there is no provision for holding the beans at a given temperature and/or decreasing the rate of heating during the roast cycle. As a result, prior art roasters cannot always provide for a complex roast profile. Likewise, prior art roasters carry out quenching the roasted beans in a single stage cycle carried out in the roasting chamber itself While such in-chamber, single stage quenching does produce an initial relatively quick drop in the temperature of the roasted beans, the present invention recognizes that residual heat in the roasting chamber, air delivery system, and other relatively massive components of the fluidized bed apparatus can slow the further cooling of the beans and thereby compromise the flavor profile of the roasted coffee.
As will be explained in greater detail hereinbelow, the present invention provides a fluidized bed coffee roasting system and method which can allow a user to implement a complex roast profile. Also, the system of the present invention can implement a two stage quenching cycle, wherein the roasted beans are first partially cooled in the roasting chamber during a first stage of the cycle and then discharged to a fluidized bed quenching system, which is separate from the roasting chamber, and in which they are rapidly cooled to an ambient temperature in a second stage of the cycle. These and other features and advantages of the present invention will be apparent from the drawings, description and discussion which follow.